Polishing pad and polishing method

ABSTRACT

According to one embodiment, there is provided a polishing pad having a surface for the polishing processing of a polishing workpiece. Here, the polishing pad is made of a plate-shaped thermal shrinking material, and it has a half-cut portion cut to a particular depth from one principal surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2012-067679, filed on Mar. 23, 2012, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate to a polishing pad and a polishingmethod.

BACKGROUND

In the manufacturing process of semiconductor devices, as the flatteningtechnology, the chemical-mechanical polishing method (ChemicalMechanical Polishing, to be referred to as CMP) is mainly used. Usually,a groove is processed on the surface of the polishing pad used in theCMP method for feeding and exhausting the slurry to/from the polishingsurface.

However, when the polishing pad is worn off due to dressing(conditioning of the polishing pad), the depth of the groove graduallybecomes shallower and the shape of the groove changes, so that thepolishing characteristics also change. That is, the groove formed on thesurface of the polishing pad is a major factor in determining a lifetimeof the polishing pad.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating an example of theconstitution of the CMP apparatus for which the polishing pad of theembodiment of the present disclosure is used.

FIGS. 2A and 2B are partial cross-sectional views illustrating anexample of the constitution of the polishing pad in the embodiment.

FIG. 3 is a top view illustrating an example of the constitution of thepolishing pad in the embodiment.

FIGS. 4A and 4B are schematic cross-sectional views illustrating thestate of the polishing pad after a certain time of use.

FIGS. 5A and 5B are schematic partial cross-sectional views illustratingthe state of use of the polishing pad after a certain time of use of thepolishing pad having a conventional groove structure in a comparativeexample.

DETAILED DESCRIPTION

In general, according to one embodiment, the polishing pad and polishingmethod of the embodiment will be explained in detail with reference toattached figures. However, the present disclosure is not limited to theembodiment.

The embodiment has an aim to provide a polishing pad and a polishingmethod for reducing variation of polishing characteristics even when apolishing pad is polished.

According to the embodiment, there is provided a polishing pad having apolishing surface for polishing a workpiece. The polishing pad is madeof a plate-shaped thermal shrinking material, and it has a half-cutportion cut to a particular depth from one principal surface.

FIG. 1 is a schematic side view illustrating an example of theconstitution of the CMP apparatus for which the polishing pad of theembodiment is used. FIGS. 2A and 2B include schematic partialcross-sectional views illustrating the constitution of the polishing padin the embodiment. FIG. 2A shows the normal state and FIG. 2B shows thestate in the polishing operation. FIG. 3 is a top view illustrating anexample of the constitution of the polishing pad in the embodiment.

The CMP apparatus includes a rotatable polishing table 21, a polishingpad 22 bonded via a bonding layer, not shown in the figure, on thepolishing table 21, a polishing head 23 arranged on the polishing pad 22and that holds a semiconductor substrate or other polishing workpiece20, a chemical solution feeding nozzle 24 for feeding polishing slurry241 or other chemical-solution in the polishing operation, and a dresser25 made of, for example, a diamond disk or the like, arranged above thepolishing pad 22 for dressing the polishing pad 22.

The polishing head 23 holds the polishing workpiece 20 by a vacuum chuckholder or similar part so that the surface for polishing faces thepolishing pad 22 on the polishing table 21. The polishing head 23 andthe dresser 25 have a structure such that they can be rotated in thesame plane as the polishing table 21 and, at the same time, they can bedriven to move in the direction perpendicular to the surface of thepolishing table 21 so that the surface of the polishing head 23 ordresser 25 can make contact with the surface of the polishing pad 22. Inaddition, although not shown in the figure, a polishing slurry feedingtank is connected with the chemical-solution feeding nozzle 24.

The polishing pad 22 in this embodiment has a half-cut portion 31. Here,the half-cut portion 31 is cut to a particular depth from the surface ofthe polishing pad 22, and it does not go through to reach the backsurface of the polishing pad 22. Here, the half-cut portion 31 differsfrom the groove in that it does not have a particular width. In thenormal state, not in the polishing operation, the two side surfaces withhalf-cut portion 31 held between them are in contact with each other. Asshown in FIG. 3, the half-cut portion 31 is formed in, for example, alattice shape on the surface of the polishing pad 22. Also, the half-cutportion 31 may be formed in a vortex shape, or concentric circular shapeor the like, instead of the lattice shape on the surface of thepolishing pad 22. The depth of the half-cut portion should beappropriate to ensure that it does not cut through to reach the bondinglayer as the underlying layer of the polishing pad 22.

The polishing pad 22 is made of a material that shrinks under the heatgenerated in the polishing operation as to be explained later. Anexample of such a thermal shrinking material is the thermal shrinkingpolyurethane. Also, the polishing pad 22 may be made of either a foamingmaterial or a non-foaming material.

In the following, a brief account will be given on the CMP processingmethod using the CMP apparatus. Here, as an example, a semiconductorsubstrate on which a silicon oxide film is formed will be taken as thepolishing workpiece 20 for explanation. In this case, it is supposedthat bumps/dips are formed on the surface of the silicon oxide film asthe surface for polishing.

Before the polishing operation, the semiconductor substrate is held onthe polishing head 23 so that the silicon oxide film faces the polishingpad 22. In addition, a polishing slurry 241 containing, for example,cerium oxide grains and a surfactant is fed from the chemical-solutionfeeding nozzle 24 onto the polishing pad 22.

As the polishing pad 23 is driven to move in the direction towards thepolishing table 21, the semiconductor substrate is pressed on thesurface of the polishing pad 22 and, while the polishing table 21 andthe polishing pad 23 are driven to rotate, the surface of thesemiconductor substrate is subjected to a polishing operation. After thestart of the polishing operation, while the polishing pad 22 and thepolishing workpiece 20 are in contact with each other, they are drivento rotate in the in-plane direction, so that friction leads to a rise inthe temperature near the surface of the polishing pad 22. Depending onthe types of polishing workpiece 20 and the polishing slurry 241 as wellas the polishing conditions, the temperature of the surface of thepolishing pad 22 may rise to about 60 to 80° C. in the polishingoperation.

As shown in FIG. 2B, because the polishing pad 22 is made of thermalshrinking polyurethane or other thermal shrinking material, due to therise in the temperature on the surface of the polishing pad 22 in thepolishing operation, the polishing pad 22 shrinks in the in-planedirection and in the direction perpendicular to the polishing surface onthe surface of the polishing pad 22. Also, as the position moves deeperfrom the surface of the polishing pad 22, the temperature of thepolishing pad 22 decreases, so that the shrinkage degree of the thermalshrinking material becomes smaller. As a result, at a particular depthd1 position from the surface of the polishing pad 22 where no thermalshrinking takes place, the side surfaces that hold the half-cut portion31 between them are in contact with each other. As the position becomesshallower (as the position moves towards the surface), the shrinkagedegree in the in-plane direction increases, so that the side surfaces ofthe half-cut portion 31 are separated from each other. Consequently, agroove 32 is formed at the half-cut portion 31. The polishing slurry 241fed from the chemical solution feeding nozzle 24 is then fed into theformed groove 32, and the polishing slurry 241 is exhausted from thegroove 32 as the polishing operation is executed.

With the progress of polishing, cerium oxide grains generated in thepolishing operation and the coagulated polishing grains formed due tocoagulation by the surfactant as well as polishing-generated chaff,etc., are accumulated in a large quantity on the polishing pad 22 andthe groove 32. As a result, clogging of the polishing pad 22 takesplace, so that the polishing speed falls. At this point, in order toeliminate this problem, a dressing treatment should be carried out.

In the dressing treatment, the surface of the dresser 25 is pressed onthe surface of the polishing pad 22 and, as the polishing table 21 andthe dresser 25 are driven to rotate, the surface of the polishing pad 22is polished. As a result, while the coagulated polishing grains andpolishing-generated chaff on the surface of the polishing pad 22 areremoved, dressing is carried out in this treatment. As explained above,in the CMP treatment, the polishing treatment and dressing treatment arecarried out.

FIGS. 4A and 4B include schematic cross-sectional views illustrating thestate of use after a certain time of use from the start of use of thepolishing pad. FIG. 4A is a schematic cross-sectional view illustratingthe initial state before use. FIG. 4B is a schematic cross-sectionalview illustrating the state during the polishing treatment after acertain time of polishing. After use of the polishing pad 22, thepolishing pad 22 with the initial state shown in FIG. 4A becomes thestate shown in FIG. 4B, with a reduced thickness of the polishing pad 22due to the thermal shrinking and dressing treatment. When the polishingtreatment is carried out in such a state, as explained above, due to theheat generated in the polishing, the portion of the polishing pad 22from the top surface to a particular depth is deformed due to thermalshrinking, and groove 32 is formed on the half-cut portion 31. The depthd2 of the groove 32 formed in this case is similar to the depth dl ofthe groove 32 formed using the polishing pad 22 in the initial stateshown in FIG. 2B. The shape and size of the groove 32 as shown in FIG.4B are similar to those shown in FIG. 2B. This remains true and isindependent of the thickness of the polishing pad 22 until the positionof height d1 from the end point 311 of the half-cut portion 31 (d2)becomes the top surface of the polishing pad 22.

In this way, by using the thermal shrinking material, it is possible toensure that the shape and size of the groove 32 formed in the half-cutportion 31 are kept the same even when the thickness of the polishingpad 22 changes. As a result, it is possible to ensure a constantquantity of the polishing slurry 241 fed to the groove 32 in thepolishing operation, and it is possible to ensure stable polishingcharacteristics independent of the remaining thickness of the polishingpad 22.

FIGS. 5A and 5B include partial cross-sectional views schematicallyillustrating the state of variation over time of the conventionalpolishing pad as a comparative example due to the polishing operation.FIG. 5A is a partial cross-sectional view illustrating the state of thepolishing pad in the initial state. FIG. 5B is a partial cross-sectionalview illustrating the state of the polishing pad after use for a certaintime. As shown in FIG. 5A, for the conventional polishing pad 22, agroove 35 with a width of W (>0) and depth of d3 is formed on it. Asshown in FIG. 5B, after use for a certain time, because the polishingpad 22 is worn off due to the dressing treatment or the like, the groove35 on polishing pad 22 has a width of W and a depth of d4.

When the polishing pad 22 is in use, the polishing slurry 241 enters thegroove 35 while the polishing operation is carried out. However, thegroove 35 shown in FIG. 5A is deeper than the groove 35 shown in FIG.5B, so that the polishing slurry 241 is fed into the groove 35. As aresult, in the polishing operation, the quantity of the polishing slurry241 changes corresponding to the difference in depth (d3−d4) of the twogrooves 35, so that a significant difference takes place in thepolishing characteristics between them. That is, because the polishingcharacteristics depend on the thickness of the polishing pad 22, it isnecessary to carry out the polishing operation with the thickness of thepolishing pad 22 taken into consideration.

On the other hand, for the polishing pad 22 in the embodiment, the shapeand size of the groove 32 formed for the half-cut portion 31 in thepolishing operation are kept constant and independent of the thicknessof the polishing pad 22. Consequently, the quantity of the polishingslurry 241 enclosed in the groove 32 during the polishing operation iskept constant. As a result, there is no difference in the polishingcharacteristics depending on the thickness of the polishing pad 22, andit is possible to realize stable polishing characteristics over theentire lifetime.

Also, it is possible to carryout the polishing operation underconditions without considering the thickness of the polishing pad 22.That is, there is no need to determine the optimum polishing conditionsfor each thickness value of the polishing pad 22. More specifically, forthe conventional polishing pad 22 shown in FIGS. 5A and 5B, the lifetimeof the polishing pad 22 is taken as the time when the depth of thegroove 35 reaches a certain level, so that the lifetime of the polishingpad 22 depends on the polishing characteristics that vary depending onthe depth and shape of the groove 35. On the other hand, according tothe present embodiment, the position of the end point 311 of thehalf-cut portion 31 is selected as the depth without going through thepolishing pad 22. Consequently, compared with the case of the polishingpad 22 having the groove 35 shown in FIGS. 5A and 5B, it is possible toprolong the lifetime. This is an effect of the present embodiment.During the period until the lifetime of the polishing pad 22 is reached,the polishing rate and evenness can be kept constant independent of thethickness of the polishing pad 22. This is another effect of the presentembodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein maybe made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A polishing pad comprising: a surface forpolishing processing of a workpiece, and a half-cut portion cut to aparticular depth from one principal surface, wherein the polishing padis made of a plate-shaped thermal shrinking material.
 2. The polishingpad according to claim 1, wherein the thermal shrinking material is athermal shrinking polyurethane.
 3. The polishing pad according to claim1, wherein the half-cut portion has a lattice shape, vortex shape, orconcentric circular shape.
 4. A polishing apparatus comprising: arotatable polishing table; a polishing pad provided on the polishingtable; a feeding nozzle configured to feed a slurry to the polishingpad; a polishing head that can hold a workpiece; wherein the polishingpad comprising: a surface for polishing processing of the workpiece, anda half-cut portion cut to a particular depth from one principal surface,wherein the polishing pad is made of a plate-shaped thermal shrinkingmaterial.
 5. The polishing apparatus according to claim 4, wherein thethermal shrinking material is a thermal shrinking polyurethane.
 6. Thepolishing apparatus according to claim 4, wherein the half-cut portionhas a lattice shape, vortex shape, or concentric circular shape.
 7. Apolishing method comprising: feeding slurry to a principal surface of aplate-shaped polishing pad while the polishing pad is driven to rotatein the in-plane direction, the polishing pad being made of a thermalshrinking material and having a half-cut portion cut to a particulardepth from one principal surface, and polishing a surface of a workpiecewith being in contact with the principal surface of the polishing pad,shrinking the polishing pad in the region from the surface of theprincipal surface of the polishing pad to a particular depth, therebyforming a groove with a certain shape and a certain size on the contactportion of the half-cut portion with the polishing workpiece.
 8. Thepolishing method according to claim 7, wherein the thermal shrinkingmaterial is a thermal shrinking polyurethane.
 9. The polishing methodaccording to claim 7, wherein the half-cut portion has a lattice shape,vortex shape, or concentric circular shape.